Transmission control



Filed Oct. 6, 1931 I INVENTOR 0. ac/hell BY WK ATTORNEY 10 wire circuit connectedto an eiitending tw rectum-i119 1 1,986,515

v UNITED STATES "PATENT OFFICE 1 p 1" :96,5 l p t TRANSMISSION CONTROL 1 Doren Mitchell, Martinsvill e, N.:J., assignor to American Telephone and Telegraph Oompany,

a corporationoi New York e 1 Application Octoberfi,1931, SerialNo. 567,326

' comma; (oi. re-nor;

' This invention relates tosystems for the transcuit comprising a one-way path L1 adapted for mission of energy, such as telephone Systems, over transmission from left to right; and afsecondonewhich are transmitted the electrical' waves-repre way path L2 adapted for transmission from right senting speech. More particularly, the invention to left. At its left, end, the four-wire circuit is 5 relates tofour-wire' telephone circuits connected connected-to a two-wire line L through the usual 5 to a two-wire line, in which transmission is conarrangement-of hybrid coil H and an artificial trolled by switching devices responsive to the network-"which imperfectly balances the impedvoice'waves. 1

" ance of fthe' line L: It will be understood that In the usual terminal arrangement of the four wire circuit mayfbe extended to the H rightby a m'utable link, such as a radioilink. 1 1 10 line, the transmitting path is adapted for-transf one-way paths L iand L2 are equipped missioniromthetwO-Wirieline, and the receiv with" "the" usual one-way amplifiers and delay ing path is adapted for transmission tothat line. circuits;- and-there is schematically indicated ap- These two paths of the four-wire circuit are'conparatus for controlling the volume in these two nected to the twowire linethrough a hybridcoil," paths, u e 1 g 5 and the impedance'o-ff the twe-waeimeeen be fqyflhe-jpath Li 10f the four-wire circuit, which only imperfectly balanced by an artificinetmay be termed the transmitting path, is norwork. 1 i I *7 mallyf'disabled at the point a'for the purpose of e The transmittingpath of thefour-wire cirsuppressing singing; An amplifier-detector AD1 cuit is usually maintainedin a normal-,"ormom' is;connectedjacross the path L1 at the point D; 20

50 the following description "isread with'refer'ence:

operating, condition of disability, in order 'that The'output circuit of this amplifier detector in-' singing may be avoided; arrangementsar'e then cludes the winding of a master transmitting relay provided whereby voice energy -in the transmit: MSanduthewinding' W1 of a marginal relay S1 ting path causes the-removal of this normal dis-- to hefdiscussed hereinafter. When the relay MS ability and the simultaneous disabling-"cr me operates; {a circuitis closed through battery B 25 receiving path. and thewi'nding'sof relays SS and ES. The relay Since the balanceibetween thetwo-wire line SS controls the. singing suppressing disability at and the artificial network is not perfectywhen point a' in the path L1, while the relay ES is deenergy travels to the tWo-wi-re'line over theresigned to disable the receiving path L2 atpoint c.

ceiving path of the four-wire circuitQa part ofthis A second fl amplifier -detector ADz is connected 30 energy is usually reflected over the transmitting across path L2 atpoint d and includes in its outpath, and if this echo energy is of sufficiently put circuit the windings of relays S and S and high value to cause operation of the transmisthewinding W2 of the above mentionedmarginal sion control apparatusresponsive to energyin there1ayjS1.

5 transmitting path, a serious condition offfalse [The apparatus described above is, with the operation and interference with speech transexception er the marginal relay S1 and the, relay mission isencountered. S, the apparatus usually provided in a four- The principal object" of thepr'esent invention wire circuit for the suppression of singing and is the prevention or substantialreduction of'such echoes. When a subscriber connected to the fals Operation y echo ene y ue to l Oo olj two-wire line L talks, the energy representing 40 y g two-wire balance. i i v his voice travels over the path L1. At the point In acc mp n the abovefstated bj t b ,;avpflortion (111m energy is'diverted to operate app a t u s a volume regulator t r the 'amplifier'detector AD1. Unless control of 1 ceiving path and Provides folithe c i noi the circuithas been taken by the subscriber at receivedvolume when 9 m v we 'i t the right end of the system, the operation of 45 energy in the receivtngrpathand the f c e n amplifier-detector AD1 results in the operation 53 fi ggi gggs in P f a tj fii of relay MS, which operation in turn results in i 1 v 1 w i theoperation of relays SS and ES. The opera- The mventlon W111 be clearly undergtoodlwhen tion of relay SS removes the disability at i t a and clears the path L1 for the transmisto'the accompanymg drawlnawhich shows d a- R v 1 v grammatically one suitable form (11 the applicant's Slon Outgomg V0106 gy, a suitable determinalarrangement. I aYPBmgJIItIOdUCGG by the delavcircuit to m- ""With reference to the details of the drawing; u he i e removal a t-t s lw p vhe 55 there is shown one terminal of a'four-wire ciroperation of relay ES places a disabihty on the 55 control has been taken by the subscriber .at the ;j

left end of the system, the incoming waves are cut off at point in the path- L2. If such control has not been taken, however, the voice energy passes on toward the line L, and a small portion of this energy is diverted at point 41 to operate the amplifier-detector AD2. The operation ofthis amplifier-detector tends to energize the windings of relays S and S and also the winding. W2 of the marginal relay S1, which winding, as indicated on the drawing, is smaller than the winding W The relay S should be made considerably more sensitive than the relay S, and when so adjusted,

I will operate on substantially any incoming energy. If the incoming energy is of sufiiciently high volume, it will result notonlyin the operation of relay S but also in the operation of relay S and the appreciable energization of winding, W2 of relay S1; When relay S operates, the output circuit of amplifier-detector AD1 is broken; this results in, the prevention of theoperation of relays MS, SS and'ES in response to later arriving energy in the path L1.

Athree-electrode. vacuum. tube T is-conneoted across the receiving path L2 to fornia variable bridged impedance. Asuitable negative voltage is'impresesdon the grid of tube T from battery B. Thefunction of theapplicants arrangement of relays and associated apparatus is to reduce the bridged impedance of the tube T andthus in-. crease the loss introduced in the path L2, but to controlled thereby. To assist in the accomplishment of, this function, the applicant utilizes a condenser C potentially in circuit with a resistance R1 andthe battery 3'."

Let it. be assumed that the energy comingin over path L2 is too weak to operate relay S but is reflected back over path L1 at a value. suiiiciently high to operate relay, S1 through the energization of winding W1. The energy in path L2, though too weak to operate relay S, will operatev relay S and partially prepa're a charging circuit for the condenser C. When the echo energyin path L operatesrelay S1, this charging circuit is completed and the condenser C renders the voltage impressed on the grid of tube T less negative, and the bridged impedance is lowered; The re sult is an increase of the 'loss introduced in Since relay S is made very sensitive, it will operate in response to any appreciable energy passing the point 0 in the path L2; in other words, the relay S will operate unless the path L2 has been blocked at point e in response to voice'energy in path L1. The operation of relay S1 depends, of course, on the relation of the currents in the windings W and W2. This relation'in turn is dependentupon the relation between the energy in path L2 at point d and thereflected energy in path L1 at point b. If the'value of the energy in path L1 is sufficiently high. with-respect to the value ofthe energy in path L2, relay S1 will operate and the loss introduced in the path L2 by the tube T will be increased. Thus the applicants arrangement serves to reducethe volume in path L2 and thus, indirectly, to reduce or eliminate the chance of false operation of the transmitting relays, but avoids this reduction of volume in the receiving path when such reduction is not necessary be cause of the balance between line L and the network While theinvention has been disclosed in one specific embodiment for the purpose of illustration, it will be understood that such disclosure is not necessarily limiting but that the scope of the invention is determined by the appended a ms.

What is claimed is: 2

. 1. In a-system for the transmission of energy, a two wire-line, a four wire ,circuit connected thereto and including a receiving path for transmissionto said line and a transmitting path for transmission therefrom, means in said receiving pathfor introducing a variable loss therein, control means for adjusting said loss introducing means to vary the loss introduced thereby, means forlimiting the operation of said control means to a predetermined relation between the energy insaid-receiving-path and the energy in said transmitting path which is'an echo of said firstmentioned energy,and means for further limit- Qhe operation. of said; control means to a predeterminedgor lower level of energy in said receiving path. I I

2. In afour-wire circuit for the two-way transmission-of energy, a first path adapted for transmission in one direction, a second path adapted for transmission inthe opposite direction, means for connecting said paths and for extending the transmission of energy such that energy transmitted over said second path will be partially reflected over said first path as echo, means in said second path for introducing a variable loss therein, and means for adjusting said loss introducing means to vary the loss introduced thereby in response to a predetermined margin of value between theenergy in said second path and the echo thereof in said first path and only when the energy in said second path is of a predetermined or lower level. i p

3. In a four-wire circuit for the two-way transmission :of energy, a first path adapted for transmission in one direction, a second path adapted for transmission in the opposite direction, means for connecting said paths and for extending the transmission of energy such that energy transmitted. over said second path will be partially reflected over said first path, means in said second. path for introducing a variable loss therein, means for normally disabling said first path, means responsive to non-reflected energy in said first path for removing the normal disability therefrom and for disabling said second 1,986,515 path, and means for adjusting said loss introducing means to vary the loss introduced thereby in response to a predetermined margin of value between the energy in said second path and the; reflected energy in said first path and only when including a two-wire line, a four-wire circuit comprising a transmitting path adapted for transmission from the two-wire line and a receiving path adapted for transmission to said line, means for interconnecting said paths and said line such that energy transmitted over said receiving path is partially reflected over said transmitting path, and means responsive to energy in said transmitting path for controlling the transmission over the system; the method of preventing false operation of said transmission control means which consists in introducing a loss in said path in accordance with the margin between the energy transmitted over said path and the energy reflected over said transmitting path as echo of said first-mentioned energy, and limiting such variation to a condition in which the energy in said receiving path does not exceed a predetermined level. n

DOREN MITCHELL.

variable loss in said receivingpath, varying the i 

